Heat exchanger



July 2, 1957 J. A. FABREGAS ETAL HEAT EXCHANGER Filed Aug. 3, 1953JOSEPH A. FABREGAS. MAX E.UNDERWOOD.

INVENTORS.

ATTORNEY i-atented July 2, 1957 Fice HEAT EXCHANGER Joseph A. Fabregas,Cassadaga, and Max E. Underwood, Dunkirk, N. Y., assiguors to AlcoProducts, Inc., New York, N. Y., a corporation of New York ApplicationAugust 3, 1953, Serial N 0. 372,119

6 Claims. (Cl. 257-32) This invention relates to heat exchangers andparticularly to exchangers of the shell and tube type which are providedwith sub-coolers.

The trend in high pressure heat exchangers, as exemplified by a feedwater heater, is to employ a subcooling section to extract heat from thesteam condensate thus increasing the total heat recovery from the steam.Steam supplied to sub-cooled exchangers must be isolated from thesub-cooler or the coolers efliciency is impaired. For that purpose avalve or bafile is usually arranged between the condensing section andthe sub-cooler so that a water seal is provided between the two to keepthe steam out of the sub-cooler.

Any such water seal should leave exposed to the steam as much of thetubes as possible so that the maximum tube surface may be utilized forheat exchange. Moreover, the sub-cooler should be maintainedsubstantially full of condensate. Meeting these requirements within theconfines of a normally sized heat exchanger without resort to valves ormechanical controls to drain off the condensate from the condensingsection and still provide for fluid movement in the most eflicient heatexchange manner has heretofore been considered impossible.

The principal object of the present invention is to provide a heatexchanger of the described type in which a continuous drain ofcondensate from the condensing section to the sub-cooler is effectedthrough a clear unrestricted passage without resort to the use of valvesor other mechanical controls.

Another object of the invention is to provide a vertical heat exchangerof the channel-down type in which the condensate is kept at a low levelin the condensing section and at a high level in the sub-cooler withmeans to elfect a continuous drain of the condensate from the former tothe latter without resort to valves or other mechanical controls.

Still another object is to provide a heat exchanger construction inwhich a continuous draining movement of condensate from the condensingsection to the sub-cooler is produced by utilizing a pressuredifferential between the sub-cooler and condensing section to create asiphon between the condensing section and the sub-cooler while at thesame time a water seal is maintained at the intake end of the siphon tokeep steam out of the sub-cooler.

A further object is to provide such a construction which avoidsexpansion dificulties by having it mounted upon the floating tubebundle.

Other and further objects of the present invention will be apparent fromthe following description, the accompanying drawing, and the appendedclaims.

In the drawing, a vertical shell and tube type heat exchanger of thefeed water heater class is shown schematically with the sub-cooler ofthe invention arranged therem.

The heat exchanger illustrated is a feed water heater of the shell andtube type and comprises a vertical shell 19, a bundle of U-tubes 11(only one of which is shown although the tubes need not be U-shaped),and a channel or water box 12 whose upper wall 13 acts as a tube sheet.Channel 12 is divided by wall 14 into two compartments 15 and 16. Feedwater to be heated is supplied through inlet nozzle 17 to compartment 15whence it passes upward into the tubes. Steam supplied through inletnozzle 18 encounters the tubes and gives up heat to the water. The steamis condensed and drawn off through outlet nozzle 19 in the manner laterdescribed. The heated water passes down into compartment 16 whence it isdrawn off through outlet nozzle 21 to a point of use. A plate 22 may bearranged opposite steam inlet nozzle 18 to prevent a direct blast ofsteam against the tubes.

The shell contains upper and lower condensing sections 23 and 24 and acondensate sub-cooler generally indicated at 25. The shell isforeshortened in the drawing as the upper condensing section 23 is ofconsiderable height. The sub-cooler 25 comprises an open top condensatereservoir 26 formed by a wall 27 which encloses the lower portion of theintake ends of the U-tubes. Wall 27 is supported by channel wall 13 andis spaced from the shell by integral radial flange 28 which ispreferably secured to the latter although wall 27 may be entirelysecured to wall 13 and still have suitable condensate outlet means. Theupper end of reservoir 26 is open for the reception of condensate andits lower end is in communication with draw-oil nozzle 19. A series ofbaflles 29 extend inwardly into the reservoir from the wall 27 toprovide a restricted flow zone to maintain a path of maximum distancefor the condensate flowing down through the sub-cooler to draw-offnozzle 19.

Steam condensed in that part of the upper condensing section 23 which isvertically above the sub-cooler drops directly into the reservoir. Steamcondensed in the remainder of the upper condensing section 23 iscollected by darn or plate 31 and pours into the sub-cooler reservoir26. Plate 31, which is arranged above and to one side of the sub-coolerpreferably overlaps the open end and is formed with holes shaped andarranged so that it may be mounted on the tube bundle in fluid tight relation thereto. A rim portion 32 is formed on the plate and extendsalmost completely around its periphery. The rim is interrupted at theside of the plate adjacent the sub-cooler so that an opening is providedto permit the flow of condensate from the plate into the sub-cooler.Thus most of the condensed liquid is funneled or directed into the opentop of the sub-cooler. Steam which is not condensed in the uppercondensing section 23 passes under plate 31 and reaches the lowercondensing section 24 where it is condensed and collected in the bottomof the lower condensing section 24 to form a second reservoir or sealingpool above the channel wall 13.

Offset from sub-cooler wall 27 and connected thereto is a second wall 33which extends downwardly to terminate a short distance above channelwall 13 in the preferred embodiment. An opening 34 is formed insubcooler wall 27 opposite the upper portion of offset wall 33. Wall 33extends a substantial distance along wall 27 and is joined thereto atits ends so that a passage 35 is provided to establish communicationbetween opening 4 and the condensate reservoir formed in the lowerportion of the lower condensing section. Condensate collected in suchlower section passes through passage 35 into the sub-cooler reservoir bya siphon action.

Within the sub-cooler, the fluid pressure at the top of the reservoir isgreater than at the outlet nozzle 19. The reason for the pressuredifferential is that the condensate, in following its circuitous pathdown the baffled length of the sub-cooler to nozzle 19, is subjected tofriction and orifice losses. These losses are, however, absent in lowercondensing section 24 so that the pressure at the bottom of this sectionis higher than at the corresponding level within--the sub-coolersection. Conditions for As previously stated in the objects of theinvention, it; is desirable to, keep asmuch as possible *of the-tubes1n' the condensing sections 23 and 24 exposed to the steam;

in order that their full condensing capacity may be utilized. The tubescannot be exposed below the end of ofiset wall'ffi; however, .becausesteam would then pass into the sub-cooler andimpair its efficiency.Consequently, a level of condensate sufiicient to safely. cover theintake'opening of. passage 35 at maximum operating conditions isrequired. This then locates the position or height of opening 3 i. e. itis determined for maximum operation of the heat exchanger by consideringcertain variables as set out below. At less than maximum operatingconditions, .thelevel of the condensate in lower condensing section 24rises to adjust itself to the fluid head required for continuousoperation of the siphon effect. It is also. desirable that. thesub-cooler reservoir be kept'nearly full so that the temperature of thewater entering at nozzle 17 will beas close as possible to thetemperature of the condensate passing out through nozble i9. Maximumextraction of heat is thus insured.

The location of opening 34 and the level of the water maintained in thereservoir at the bottom of condensing section 24 depends on theconditions of pressure balance as determined for each particularconstruction. Factors to be considered in this connection are the designof reservoir wall, baifle size and arrangement, static head, andexpected load conditions.

in operation, open ended sub-cooler reservoir 26 is maintainedsubstantially full of hot condensate by dam 31 to warm .the incomingwater which is further heated as it passes through the U-tubes tocompartment 16 and outlet nozzle El. By automatic adjustment of liquidheads, a water seal is maintained by the pool of condensate incondensing section 24 which covers the intake opening of passage 35 tokeep steam out of the subcooler. By .means of the siphon actiondescribed, the level of the condensate in lower condensing section 24 ismaintained at a point determined by load conditions and the excesscondensate is carried into the sub-cooler reser voir where heat isextracted from it. It thus is apparent that maximum tube area incondensing section 24 is exposed to the steam during the second or hightemperature pass of the fluid to be heated.

When the unit is in operation at maximum capacity, the flow ofcondensate through the sub-cooler is at a maximum rate. Hence thecondensate flow through pas sage 35 is likewise at maximum. Thecondensate in condensing section 24 is at its lowest level so thatalmost all the surface of the tubes is available for condensing surfaces. At less than maximum performance, the condensate flow through thesub-cooler diminishes which, in turn, diminishes the condensate flowthrough siphon passage 35. The condensate level in section 24,accordingly, rises to cover a portion of the tube surface. Since theperformance is not at a maximum, the slight loss of effective surface isnot of consequence. It thus appears that the invented constructionautomatically compensates for changes in load and performance withoutthe use of separate controlling devices. By useof the open endedsubcooler and dam to direct the condensate, the sealing means normallyused to close the top of the subcooler is eliminated.

While there has been hereinbefore described an approved embodiment ofthis invention, it will be understood that many and various changes andmodifications in form, arrangement of parts and details of constructionthereof may be made without departingfrorn the.

Additional. heat may;

modifications as falhwithinthescope of the appended claims arecontemplated as a part of this invention.

What we claim is:

l. A heat exchanger comprising a vertical shell having a steam inlet, aplurality of tubes extending vertically of said shell, a channelstructure connected to said shell and associated with said tubes toprovide for the passage of fluid therethrough, a vertical subcoolerwithin the shell enclosing p211'iy0ftho tubes anddaeing-open; at theupper end to communicate with the shell interior, a condensate outletfrom said subcooler, and a passage connecting the lower end of the-shellinterior with a higher interior point of the subcooler.

2. A heat exchanger comprising a vertical shell having a steam inlet, aplurality of tubes extending vertically of said shell, a channelstructure connected to said shell and associated with said tubes toprovidefor thepassage of fluid therethrough, a verticalsubcooler.,within the shell enclosing part of the tubes and being openatv the upper end to communicate with they shell interior, a condensateoutlet from said subcooler, means spaced above said open end to directcondensate into the subcooler, and a passage connecting the lower end ofthe shell interior. with a higher interior point of the subcooler.

3. A heat exchangercomprisinga vertical shell having a steam inlet, aplurality of tubes extending vertically of said shell,'a channelstructure connected to said shell and associated with said tubes toprovide .for the passage of fluid therethrough, a vertical subcoolerwithin the shell enclosing part of the tubes and being open at the upperend to communicate with the shell .interior, a condensate outlet fromsaid subcooler, means carried by the tubes and spaced above said openend to direct condensate into the subcooler, and a passage connectingthe lower end of the shell interior with a higher interior point-of thesubcooler.

4. A heatexchanger comprising a vertical shell having a steam inlet, aplurality of tubes extending ,vertically of said shell, a channelstructure connected to said shell and associated with said tubes toprovide for the passage of fluid therethrough, a vertical subcoolerwithin the shell and enclosing a portion of the inlet ends of the tubes,said subcooler being open at its upper end to the shell interior, meansspaced above said open end to divide the shell interior into an upperand lower condensing section, said means collecting condensate from saidupper section and directing it into the open end of said subcooler, asecond condensate reservoir at the bottom of the shell adjacent thesubcooler, and a passage extending from the second reservoir to thesubcooler reservoir to siphon condensate from the second reservoir tothe subcooler reservoir.

5. A heat exchanger comprising a vertical shell having a steam inlet, aplurality of tubes extending vertically of said shell, a channelstructure connected to said shell and said tubes and having meansproviding for the passage of fluid through said tubes-in a plurality ofpasses, a vertical subcooler occupying a portion of the shell crosssectional area and supported by said channel and enclosing all of thetubes in the first pass for a portion of their length, said subcoolerbeing open at its top to the interior of the shell, means spaced abovesaid open end and substantially occupying the rest of said shell crosssectional area to direct condensate into the subcooler, and a passageconnecting the lower end. of the shell interior with a higher interiorpoint of the subcooler.

6. A heat exchanger of the vertical channel-down type comprising a shellhaving a steam inlet, a plurality of tubes extending vertically of saidshell, means for directing fluid in a plurality of passes through thetubes, a vertical subcooler supported by the channel enclosing all ofthe tubes .in the first pass for a portion of their length and.occupyinga part of .the. lower portion of the shell,

said subcooler being open at its top to the interior of the shell, aseries of circuitous flow baffles in the subcooler, a condensatecollecting plate carried by the tubes and spaced above the subcoolerover the unoccupied lower portion of the shell, and an enclosed passageconnecting the lower unoccupied portion of the shell interior with theinterior of the subcooler at a predetermined height from the lower endthereof.

References Cited in the file of this patent UNITED STATES PATENTS FraserDec. 17, 1946 Worn et a1 Nov. 29, 1949 Kirkpatrick Dec. 1, 1953 ByerleyJan. 19, 1954 Kirkpatrick Nov. 8, 1955

